I. Field of the Invention
The present invention relates to a method for controlling a continuous rolling mill and to a control apparatus therefor, wherein exit strip dimensions, such as thickness, are changed during rolling so as to obtain rolled products having different dimensions.
II. Description of the Prior Art
In the iron and steel industry, manufacturing equipment tends to become large in an effort to improve productivity. Along with this tendency, the weight of the slab or the sheet bars supplied to continuous tandem mill plants is also increasing. Therefore, the unit weight of coils manufactured by such continuous tandem mills increases accordingly. However, since users require steel plates of various sizes, a control technique is required to change the exit strip size, that is, the size of a product, during rolling without degrading productivity.
A method is conventionally proposed to control a continuous tandem cold mill as follows. The pass schedule before the size change is defined as schedule A. Under schedule A, the exit strip thickness, the roll gap, and the roll speed are not changed. The pass schedule after size change is defined as schedule B. The schedule operating during the transition period while changing the schedules from A to B is defined as schedule C. The schedules A to C are computed before rolling in accordance with setting operations (operations for setting the roll gap and the roll speed in accordance with the capacity of the equipment, the material used, the the strip to be rolled as the final product). When a size changing point X reaches each of the strands of the continouous tandem cold mill, the schedules A, C and B are performed in the order named, so that the roll gap and the roll speed are changed to obtain strips of different size.
In the control method of the type described above, the roll gaps and roll speeds must be computed in advance for the schedules A, B and C. The control is independent of the rolling conditions and is performed in accordance with the preset values. Therefore, when changes such as resistance to deformation (caused by material hardness, material temperature or a friction coefficient between the roll and material), a difference between the entry and exit strip sizes, a forward slip, or a rolling force occur during the rolling process, an error will occur in the product.